This invention relates to a method and apparatus for building a laminate 10A and in forming a subassembly 10 for a pneumatic tire from unreinforced tire components.
Historically, the pneumatic tire has been fabricated as a laminate structure of generally toroidal shape having beads, a tread, belt reinforcement and a carcass. The tire is made of rubber, fabric, and steel. The manufacturing technologies employed for the most part involve assembling the many tire components from flat strips or sheets of material. Each component is placed on a building drum and cut to length such that the ends of a component meet or overlap creating a splice.
In the first stage of assembly the carcass would include one or more plies, and a pair of sidewalls, a pair of apexes, an innerliner (for a tubeless tire), a pair of chafers and perhaps a pair of gum shoulder strips. Annular bead cores can be added during this first stage of tire building, and the ply or plies can be turned around the bead cores to form the "ply turnups."
The carcass components (excluding the bead cores) would be either "butt spliced" or "lap spliced." A butt splice has the component ends joined but not overlapped, a lap splice has overlapping ends.
This intermediate article of manufacture would be cylindrically formed at this point in the first stage of assembly. The cylindrical carcass is expanded into a toroidal shape after completion of the first-stage of tire building. Reinforcing belts and the tread are added to the intermediate article during a second stage of tire manufacture, which can occur using the same building drum or work station or at a separate shaping station.
During the expansion of the carcass, tensile stresses are imposed on the spliced and uncured components of the tire carcass.
In the case of automobile or light truck tires, lap splices were preferred because the splice remained intact whereas butt splices would tend to open or fail. Even with the good adhesion of the lap splice the cords adjacent the splice tended to be stretched compensating for the overlapped two layers of cords at the splice. This localized stretching creates a non-uniformity that is readily visible under x-ray, ultrasonic display or by physically cutting the tire and visually inspecting it.
The tire designer, in order to prevent the creation of tire uniformity problems has historically insured that the splices of the various layers of components were not circumferentially aligned. This non-alignment of splice joints was believed to improve the carcass overall durability and uniformity, as measured by the amount of force variation and the balance of the tire. Tire engineers also have believed that tire uniformity could be improved if these discontinuities were deliberately circumferentially spaced around the carcass. This meant that each component had to be applied to the ply at the tire building station where each component was cut and spliced in a spaced order.
A U.S. patent issued in 1917 taught the use of an apparatus to assemble strips to form a tire tread subassembly. U.S. Pat. No. 1,353,934 issued in 1917 teaches in order to create the strips of proper width and location the components were required to be trimmed at the apparatus. This tread subassembly included a cord reinforced belt and optionally could include a pair of sidewalls. This method of assembly required the sidewalls to be turned down upon assembly to a tire casing which one skilled in the art would readily appreciate is very difficult in that the unreinforced sidewall cannot conform to the compressive stresses of being turned radially inward without a high likelihood of localized buckling. This created tremendous non-uniformities in the tire and therefore has been heretofore abandoned as a viable method of tire assembly.
The subject matter of this patent application completely reverses this conventional wisdom as it relates to tire subassembly construction. The tire subassembly is manufactured with numerous unreinforced components being formed and adhered to a conveying carrier member or tire component without requiring any secondary trimming thus forming a laminate structure which can be wound onto rolls or spools for subsequent use at the tire building station. The laminate can then be cut using a novel cutting technique which results in a single splice line. The tire subassembly built according to the present invention can actually decrease the tire building costs while reducing splice-related non-uniformities.
In one embodiment of the invention, the subject matter of this patent application completely reverses this conventional wisdom as it relates to carcass construction. The carcass is manufactured with numerous components being formed and adhered to a conveying ply thus forming a laminate structure which can be wound onto rolls or spools for subsequent use at the tire building station. The laminate can then be cut using a novel cutting technique which results in a single splice line. The tire carcass built according to the present invention can actually increase the tire burst strength while reducing splice-related non-uniformities.